“We can, thankfully, remove one threat to the future existence of the human male from our worry list,” Alice Shabecoff writes at Environmental Health News via Scientific American. “The male Y chromosome, after dwindling from its original robust size over millions of years, apparently has halted its disappearing act.”

Shabecoff continues:

But don’t start cheering yet. Contrary to cultural assumptions that boys are stronger and sturdier, basic biological weaknesses are built into the male of our species. These frailties leave them more vulnerable than girls to life’s hazards, including environmental pollutants such as insecticides, lead and plasticizers that target their brains or hormones. Several studies suggest that boys are harmed in some ways by these chemical exposures that girls are not. It’s man’s fate, so to speak. First of all, human males are disappearing. Mother Nature has always acknowledged and compensated for the fragility and loss of boys by arranging for more of them: 106 male births to 100 female newborns over the course of human history. (Humans are not unique in this setup: Male piglets, as an example, are conceived in greater proportion to compensate for being more likely than female piglets to die before birth.) But in recent decades, from the United States to Japan, from Canada to northern Europe, wherever researchers have looked, the rate of male newborns has declined. Examining U. S. records of births for the years between 1970 and 1990, they found 1.7 fewer boys per 1,000 than in decades and centuries past; Japan’s loss in the same decades was 3.7 boys.

Boys are also more than two-thirds more likely than girls to be born prematurely – before the 37th week of pregnancy. And, despite advances in public health, boys in the 1970s faced a 30 percent higher chance of death by their first birthday than girls; in contrast, back in the 1750s, they were 10 per cent more likely than girls to die so early in their lives. Once they make it to childhood, boys face other challenges. They are more prone to a range of neurological disorders. Autism is notoriously higher among boys than girls: now nearly five times more likely, as tallied by the U.S. Centers for Disease Control and Prevention. They are more susceptible than girls to damage from very low-level exposure to lead. Yet another problem: Boys also suffer from asthma at higher rates. There’s also a stronger link between air pollution and autism in boys. What is up here? Why do boys face such a burden of physical challenges?

The answer is that the male’s problems start in the womb: from his more complicated fetal development, to his genetic makeup, to how his hormones work.